Labour MPs who receive sponsorship will have to earn it, a leading union left-winger has warned.

The incoming head of the Transport and General Workers' Union said MPs who are "too close to the gaffer" could see an end to support.

"You can't have the penny and the bun. Labour wants our support but not our view," Tony Woodley told the Spectator.

Woodley, a fierce opponent of New Labour, issued a stark warning to the 91 MPs who rely on the union for assistance.

"Our MPs must support our aims, values and priorities. We will review our links with those who don't," he said.

The prime minister is among those backed by the TGWU.

But Woodley claimed the relationship is largely one-way and should be re-examined.

"We are not going to support a person if he is totally pushing policies contrary to ours. Why should we? MPs should understand that when they buy in," he said.

"These people are quick enough when they want support. It's not just financial. We get out and work for people."

Woodley dismissed the idea of quitting the Labour Party, as some union leaders have threatened, arguing it was better to fight from within rather than "crying from the sidelines".

But he hinted that the unions could revive a tactic used by hard-left Militant supporters in the early 80s by infiltrating Labour's local constituencies.

"We may put more money in: we may affiliate more members to Labour. I have a view that if the top six unions all decided to affiliate six people each to each constituency party, boy, that would make a difference," he said.

"In some constituency parties at the moment, you might find two men and a dog turn up.''

He also issued a stinging attack on government, claiming it would have to pay more attention to dissenting voices.

"Even Tony Blair will wake up: if you want to stay in power, some time you have to start listening," he said.

"Labour is forgetting its core values. And until now I think the trade union movement has done the same."